1. Field of Invention
The invention relates to an ink-jet head for printing by ejecting ink onto an image recording medium, a method for manufacturing the ink-jet head, an ink-jet printer, and a method for manufacturing an actuator unit.
2. Description of Related Art
In an ink-jet printer, an ink-jet head distributes ink supplied from an ink tank to pressure chambers. The ink-jet head selectively applies pulsed pressure to each pressure chamber to eject ink through a nozzle. As a means for selectively applying pressure to the pressure chambers, an actuator unit having laminated ceramic piezoelectric sheets may be used.
As an example, a generally-known ink jet head has one actuator unit in which continuous flat piezoelectric sheets extending over a plurality of pressure chambers are laminated. At least one of the piezoelectric sheets is sandwiched by a common electrode common to the pressure chambers and is being kept at the ground potential. The actuator unit also includes many individual electrodes, i.e., driving electrodes, disposed at positions corresponding to the respective pressure chambers. The part of piezoelectric sheet being sandwiched by the individual and common electrodes, and which is polarized in its thickness, acts as an active layer by applying an external electric field. Therefore, when an individual electrode on one face of the sheet is set at a different potential from the potential of the common electrode on the other face, the active layer is expanded or contracted in its thickness direction by the so-called longitudinal piezoelectric effect. The volume of the corresponding pressure chamber thereby changes, so ink can be ejected toward a print medium through a nozzle communicating with the pressure chamber.
In such an ink-jet head, to ensure good ink ejection performance, the actuator unit must be accurately positioned with respect to a passage unit so that the position of the active layer defied by each individual electrode must overlap with the corresponding pressure chamber in a plan view.
In this ink-jet head, the common electrode and the individual electrodes are formed by printing conductive pastes to be the common electrode and the individual electrodes in a predetermined pattern on the piezoelectric sheets and then by heating the pastes. Generally, when the common electrode and the individual electrodes are formed by printing the pastes, the pastes are heated with the piezoelectric sheets at a high temperature exceeding the heat-resisting level of the adhesive. Therefore, the actuator unit has to be prepared separately from the passage unit which has the ink passages with the pressure chambers. The actuator unit and the passage unit would then have to be bonded to each other by means of an adhesive with the pressure chambers being positioned on the inner side.
As described above, however, the passage unit is a lamination of metallic sheets bonded with adhesive, while the actuator unit is a sintered body prepared by heat-treating conductive electrode materials and the piezoelectric sheets at a high temperature. During high temperature sintering of the actuator unit, as the size of the piezoelectric sheets increases, the dimensional accuracy of the electrodes decreases. Thus, the longer the ink-jet head is, the more difficult the positioning process is between the pressure chambers in the passage unit and the individual electrodes in the actuator unit. As a result, the manufacture yield of heads may be decreased.
Further, an external connection member, such as a flexible printed circuit (FPC), is adhered onto the actuator unit for connecting the individual electrodes and a driver integrated circuit (IC). It is, therefore, necessary to adhere the external connection member firmly to the actuator unit.
Moreover, in the above-described ink-jet head, the individual electrodes are arranged on the laminated piezoelectric sheets. In order to manufacture this ink-jet head, a series of complicated steps are required to form through holes for connecting individual electrodes located at positions overlapping in a plan view, and burying a conductive material in the through holes.